The present invention relates generally to communications devices used on helicopters and in a particular to an electrical device for reducing modulation of radio frequency signals produced by metalized surfaces of a helicopter rotor blade.
It is well known that high frequency radio signals radiated from communications equipment aboard a helicopter produce high frequency currents in the rotor blades of a helicopter. These high frequency currents are subsequently reradiated with the rotor blade functioning as an antenna. The reradiated signals, in turn, produce audio frequency modulation of the reradiated signal as a consequence of the rotation of the helicopter blades. This modulation can be in the form of both amplitude modulation and frequency modulation.
More recently, the use of high strength composite materials such as graphite composites has enabled the production of helicopter rotor blades of relatively low conductivity thereby substantially alleviating this problem. However, it has been found necessary to provide metalized surfaces on the leading edge of high strength composite helicopter rotor blades to resist abrasion and damage to the blades caused by such things as sand and dust in the air. These metalized leading edges again result in highly conductive rotating elements which produce modulation of high frequency radio signals. Prior art solutions for this problem have included isolation of the high frequency antenna from the rotor blades, use of low impedance loop or inductive antennas, and avoidance of known frequencies at which rotor modulation is troublesome. Each of these solutions present their own limitations. Therefore there still exists a need to provide a device which will significantly reduce rotor blade modulation thereby enhancing the quality of radio frequency communications to and from the helicopter.